Milky Way swallows up stream of stars

Emma Woollacott, 29th October 2012

Using the Sloan Digital Sky Survey, researchers have discovered a stream of stars believed to be the remnant of an ancient cluster slowly being ingested by our own Milky Way galaxy.

Named the Triangulum stream, it's the first of its kind found in the southern Galactic sky, a region that's been hard to examine until now because of a relative lack of deep-sky imaging there.

"The Milky Way is constantly gobbling up small galaxies and star clusters," says Yale graduate student Ana Bonaca.

"The more powerful gravity of our Milky Way pulls these objects apart and their stars then become part of the Milky Way itself."

Researchers have previously found evidence that the Milky Way is eating up dwarf galaxies. Bonaca, though, reckons that this newly-found stellar stream is the remnant of a star cluster rather than a galaxy, because it's very narrow.

"Our discovery is more of a light snack than a big meal for the Milky Way," says Marla Geha, associate professor of astronomy at Yale. "Studying this digestion process in detail is important because it gives us new insight into how all galaxies form and evolve."

The Triangulum stream could also help astronomers reconstruct how the Milky Way's mass is distributed, says the team.

Galaxies are believed to form hierarchically through the merger of smaller galaxies and still smaller star clusters, with stellar streams forming as they're ripped apart by the gravitational force of galaxies.
This process may be the main way galaxies such as the Milky Way grow in mass, the researchers say.